The Japanese society in the early 21st must be improved so that people having troubles with the functions of their hands and feet owing to aging, accident or disease can participate in the society as those having no disabilities. The wearable power assist technology exists for those who cannot move their hands and feet freely and aims at compensation for their poor functions by wearing. Specific examples of the wearable power assist technology well known now include electric wheelchairs and electric prosthetic limbs. In addition, new technology such as powered suit capable of conveniently enhancing the mobility by wearing it is proposed recently (H. Kobayashi and T. Shiiba: Basic Study on Human Robot Interaction for Motion Support by Muscle Suite: Proceedings of 2002 IEEE, Int., Workshop on Robot and Human Interactive Communication, pp. 17–22).
For such technology, a sensor for detecting an intention to move hands and feet, a sensor for detecting the stroke of motion and an actuator for assisting the motion of hands and feet are bare essentials. In particular, an actuator must be at least equal to natural muscle in properties such as speed of response, generating stress and displacement and moreover, it must be light, less noisy and safe. Actuators having such properties are required not only in the wearable power assist technology but also for apparatuses which come in direct contact with humans or human living environments, for example, pet type robots or medical electric apparatuses.
As an actuator for powered suit, pneumatic rubber artificial muscles or motors have been employed recently. Such actuators have excellent properties, but they are heavy and tend to emit a high operating noise.
In addition to such conventional actuators, there are actuators using a soft material such as organic polymer material. Among the actuators, a conductive polymer actuator using a conductive polymer such as polyaniline or polypyrrole as a material (Japanese Patent Application Laid-Open No. 20586/1990), and an ion conductive polymer actuator using an ion exchange resin as a material (Japanese Patent Application Laid-Open No. 6991/1994) have properties suited as an actuator for wearable power assist technology, because a raw material used for them are light, does not emit a high operating noise, can be driven at a voltage as low as several volts, and is soft and safe.